Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=false, idempotentHint=false, destructiveHint=false, and openWorldHint=true. The description adds genuinely useful context beyond those: the append is positional (at the end), and it documents the auth requirement (authorized account or write-scope API key). It does not cover duplicate handling or any set-size limits.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences with the core action front-loaded, followed by the ordering caveat and the auth prerequisite. No filler and nothing redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a small two-parameter mutation with no output schema and annotations covering the safety profile, the description supplies the key missing pieces: positional behavior, sibling redirect, and auth requirements. The opaque nested 'layout' object is left to the schema and the sonar_screenshot_layout_guide sibling, which is acceptable.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both set_id and layout are already documented in the schema, and the layout's 'omit for a blank screen' guidance lives there. The description adds no parameter-level detail beyond the positional 'at the end' note, so the baseline 3 for schema-carried semantics applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a precise verb and resource: 'Append a screen to a screenshot set,' which tells an agent exactly what mutation occurs. It partially differentiates from siblings by noting the append-at-end behavior and pointing to sonar_update_screenshot_set for reordering, though it does not draw a line against the other screenshot mutators (sonar_update_screenshot, sonar_create_screenshot_set).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a clear use context (appending at the end of an existing set) and an explicit redirect to sonar_update_screenshot_set when reordering is needed. It also names the prerequisite (authorized Sonar account or write-scope API key), but never contrasts this tool with sonar_update_screenshot or sonar_create_screenshot_set, so an agent must infer which sibling fits which case.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.